Light, as an external stimulus, is capable of driving the motion of micro/nanomotors (MNMs) with the advantages of reversible, wireless and remote manoeuvre on demand with excellent spatial and temporal resolution. This review focuses on the state-of-the-art light-driven MNMs, which are able to move in liquids or on a substrate surface by converting light energy into mechanical work. The general design strategies for constructing asymmetric fields around light-driven MNMs to propel themselves are introduced as well as the photoactive materials for light-driven MNMs, including photocatalytic materials, photothermal materials and photochromic materials. Then, the propulsion mechanisms and motion behaviors of the so far developed light-driven MNMs are illustrated in detail involving light-induced phoretic propulsion, bubble recoil and interfacial tension gradient, followed by recent progress in the light-driven movement of liquid crystalline elastomers based on light-induced deformation. An outlook is further presented on the future development of light-driven MNMs towards overcoming key challenges after summarizing the potential applications in biomedical, environmental and micro/nanoengineering fields.

Intelligent photoresponsive isotropic semiconductor micromotors are developed by taking advantage of the limited penetration depth of light to induce asymmetrical surface chemical reactions. Independent of the Brownian motion of themselves, the as-proposed isotropic micromotors are able to continuously move with both motion direction and speed just controlled by light, as well as precisely manipulate particles for nanoengineering.

In this work, water-fuelled TiO2/Pt Janus submicromotors with light-controlled motions have been developed by utilizing the asymmetrical photocatalytic water redox reaction over TiO2/Pt Janus submicrospheres under UV irradiation. The motion state, speed, aggregation and separation behaviors of the TiO2/Pt Janus submicromotor can be reversibly, wirelessly and remotely controlled at will by regulating the "on/off" switch, intensity and pulsed/continuous irradiation mode of UV light. The motion of the water-fuelled TiO2/Pt Janus submicromotor is governed by light-induced self-electrophoresis under the local electrical field generated by the asymmetrical water oxidation and reduction reactions on its surface. The TiO2/Pt Janus submicromotors can interact with each other through the light-switchable electrostatic forces, and hence continuous and pulsed UV irradiation can make the TiO2/Pt Janus submicromotors aggregate and separate at will, respectively. Because of the enhanced mass exchange between the environment and active submicromotors, the separated TiO2/Pt Janus submicromotors powered by the pulsed UV irradiation show a much higher activity for the photocatalytic degradation of the organic dye than the aggregated TiO2/Pt submicromotors. The water-fuelled TiO2/Pt Janus submicromotors developed here have some outstanding advantages as "swimming" photocatalysts for organic pollutant remediation in the macro or microenvironment (microchannels and microwells in microchips) because of their small size, long-term stability, wirelessly controllable motion behaviors and long life span.

Summary Inspired by astonishing collective motions and tactic behaviors in nature, here we show phototactic flocking of synthetic photochemical micromotors. When enriched with hydroxyl groups, TiO 2 micromotors can spontaneously gather into flocks in aqueous media through electrolyte diffusiophoresis. Under light irradiation, due to the dominant nonelectrolyte diffusiophoretic interaction resulting from the overlap of asymmetric nonelectrolyte clouds around adjacent individuals, these flocks exhibit intriguing collective behaviors, such as dilatational negative phototaxis, high collective velocity, and adaptive group reconfiguration. Consequently, the micromotor flocks can migrate along pre-designed paths and actively bypass obstacles with reversible dilatation (expansion/contraction) under pulsed light navigation. Furthermore, owing to the enhanced driving force and rapid dilatational area covering, they are able to execute cooperative tasks that single micromotors cannot achieve, such as cooperative large-cargo transport and collective microenvironment mapping. Our discovery would promote the creation of reconfigurable microrobots, active materials, and intelligent synthetic systems.

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Ordered mesoporous tricompound NiO−CaO−Al 2 O 3 composite oxides with various Ca content were first designed and facilely synthesized via a one-pot, evaporation-induced, self-assembly (EISA) strategy. The obtained mesoporous materials with advantageous textural properties and superior thermal stabilities were investigated as the catalysts for the carbon dioxide reforming of methane reaction. These mesoporous catalysts entirely showed high catalytic activities as well as long catalytic stabilities toward this reaction. The improved catalytic activities were suggested to be closely associated with the advantageous structural properties, such as large specific surface areas; big pore volumes; and uniform pore sizes, which could provide sufficient "accessible" active centers for the gaseous reactants. In addition, the "confinement effect" of the mesoporous matrixes contributed to stabilizing the Ni active sites during the processes of reduction and reaction, accounting for the long lifetime stabilities of these mesoporous catalysts. The modification of Ca played dual roles in promoting the catalytic activities and suppressing the carbon deposition by enhancing the chemisorption of the CO 2 . Generally, the ordered mesoporous NiO−CaO−Al 2 O 3 composite oxides could be considered as promising catalysts for the carbon dioxide reforming of methane reaction.

This work demonstrates a simple‐structured, low‐cost magnetically modulated micromotor of MnFe2O4 pot‐like hollow microparticles as well as its facile, versatile, and large‐scale growing‐bubble‐templated nanoparticle (NP) assembly fabrication approach. In this approach, the hydrophobic MnFe2O4@oleic acid NPs in an oil droplet of chloroform and hexane assembled into a dense NP shell layer due to the hydrophobic interactions between the NP surfaces. With the encapsulated oil continuously vaporizing into high‐pressured gas bubbles, the dense MnFe2O4 NP shell layer then bursts, forming an asymmetric pot‐like MnFe2O4 micromotor by creating a single hole in it. For the as‐developed simple pot‐like MnFe2O4 micromotor, the catalytically generated O2 molecules nucleate and grow into bubbles preferentially on the inner concave surface rather than on the outer convex surface, resulting in continuous ejection of O2 bubbles from the open hole to propel it. Dexterously integrating the high catalytic activity for H2O2 decomposition to produce O2 bubbles, excellent magnetic property with the instinctive surface hydrophobicity, the MnFe2O4 pot‐like micromotor not only can autonomously move in water media with both velocity and direction modulated by external magnetic field but also can directly serve for environmental oil removal without any further surface modification. The results here may inspire novel practical micromotors.

CONSPECTUS: Micro/nanomotors (MNMs) are micro/nanoscale devices that can convert energy from their surroundings into autonomous motion. With this unique ability, they may revolutionize application fields ranging from active drug delivery to biological surgeries, environmental remediation, and micro/nanoengineering. To complete these applications, MNMs are required to have a vital capability to reach their destinations. Employing external fields to guide MNMs to the targets is common and effective way. However, in application scenarios where targets are generally unknown or dynamically change, MNMs must possess the capability of selfnavigation or self-targeting. Taking advantage of tactic movements toward or away from signal sources, numerous intelligent MNMs with self-navigation or self-targeting have been demonstrated and attracted much attention during the past few years. In this Account, we elucidate the intelligent response mechanisms of such tactic MNMs, which are summarized as two main models. One is that local vector fields, including those of chemical concentration gradients, gravity, flows, and magnetic fields existing in systems, achieve the overall alignment of asymmetric MNMs via aligning torques, directing the MNMs to swim toward or away from the signal sources. Another is that isotropic MNMs may produce propulsion forces with direction solely determined by the local vector field regardless of their Brownian rotations. Then we discuss and highlight the recent progress in tactic MNMs, including chemotactic, phototactic, rheotactic, gravitactic, and magnetotactic motors. Artificial chemotactic MNMs can be designed with different morphologies and compositions if asymmetric reactions are associated with chemical concentration gradients. In these systems, asymmetric phoretic slip flows are induced, leading to torques that enable the anisotropic particles to align and exhibit chemotaxis. For phototactic MNMs, light irradiation establishes asymmetric fields surrounding the motors via light-induced chemical reactions or physical effects to generate phototactic motion. Shapeasymmetric MNMs reorient in natural fluid flows because of torques applied by the flows, inducing rheotactic movements. MNMs with either the centroid or magnetic components distributed asymmetrically maintain orientation under the torque triggered by gravity or magnetic forces, generating tactic motions. In the end, we envision the future development of synthetic tactic MNMs, including enhancement of the sensitivity of motors to target signals, increasing the diversity of chemical motor systems, and combining multiple mechanisms to endow the tactic motors with multiple functionality. By highlighting the current achievements and offering our perspective on tactic MNMs, we look forward to inspiring the emergence of the next generation of intelligent MNMs with taxis.